As already mentioned, I found this implementation here better:

    cdef double m = v[0]
    if v[1] < m:
        m = v[1]
    if v[2] < m:
        m = v[2]
    return m

I'm not sure if it is function is of use for other parts of skimage... pretty specific use case (-> 3). And the euclidean function should be removed and replaced with fabs...